Prior enterovirus infection has been implicated in pathogenesis of certain human autoimmune diseases including the idiopathic inflammatory myopathies, juvenile-onset diabetes, and cardiomyopathy, as well as noninflammatory diseases like chronic fatigue syndrome. How the elements of enteroviral infection are linked to development of post-viral disease is unclear, but the process is probably driven by factors inherent in viral and host genomes and possibly by interaction of these factors with other environmental stimuli. This proposal is focused on identifying the specific viral gene or genes that are crucial to disease induction in a well-characterized mouse model of chronic inflammatory myopathy (CIM). CIM is induced in susceptible mouse strains by neonatal infection with coxsackievirus B1 (CVB1). A panel of CVB1 variants has been produced that are myopathic (MP) or amyopathic (AMP) with respect to CIM induction and which will be used to identify the viral components that mediate CIM development. First, infectious cDNA clones from both a prototypic MP and an AMP variant will be produced. Pathogenic phenotypes of the cloned viruses will be tested in vivo to confirm that they are equivalent to the parental viruses. The two prototypic viral clones will then be sequenced to identify specific genomic differences and construct a map of putative myopathogenicity-inducing regions. Next, the functional significance of these differences will be tested by creating MP/AMP chimeras from the clones and evaluating CIM induction using a panel of five pathologic indicators. In vivo infection with reciprocal chimeras will confirm which genomic regions are coupled to CIM development. The effect of specific genetic differences will then be verified at the single nucleotide level. Myopathic regions in the remaining variants will be examined to determine if amyopathic changes in the AMP prototype are conserved or if different mutations have occurred which have the same functional effect. This will also reveal whether the dominant disease determinants have been mapped or if additional viral genes are involved. MP3, a unique variant that induces weakness in the absence of inflammation, will be examined more extensively to answer questions regarding the interrelatedness of viral genes that induce weakness and inflammation. This study will identify which determinants of the virus interact with the host to precipitate the development of chronic immunopathic disease. Focused, mechanistic hypotheses can then be developed to explore these interactions in future studies.